Allow to select packages that conflict in case we are looking for
errors. This allows 'add --force' to install (on boot) the set of
packages with minimum conflicts.

 * each package name has two sorting positions, one which causes
   install_if triggers to be run, and other for bulk dependencies
 * fix also inverted ordering of package installations

this allows quite some optimizations to running time and memory
requirements.

 * the solver no longer does look-ahead locking of names
   (could be possibly optimized later); instead names are now
   always ordered strictly to properly detect the package names
   which are unsolveable
 * basic error tests added, so we can see the most likely problem
   in dependencies easily

Packages that need (re-)installation but which are not available,
are excluded now properly.

The first found solution is the most preferred one then.

 * basic code for a backtracking, forward checking dependency satisfier
 * works better when there are tricky dependencies to solve
   (when can't just upgrade everything to most preferred versions)
 * the new code always evaluates all of 'world' constraints
   (old code just does incremental updates based on heuristics)
 * is probably somewhat slower than old code (probably unnoticeable
   difference in most cases)
 * makes easier to write support for provides and repository pinning
 * test applet and a bunch of test cases added which uses the new code
 * from the old feature set install_if is not yet implemented

This applet can be used to generate data for graphviz tools.
Useful to visualize package dependencies, and possible errors
in the repository.

Usage examples:
  apk dot gnome-desktop | tred | dot -Tpng gnome-desktop.png
    -- to generate simplified dependency chart of gnome-desktop
  apk dot --errors | dot -Tpng index-errors.png
    -- to generate chart visualizing dependency errors in index

 * fixup the help messages to align up properly
 * refresh screen width on SIGWINCH

fixes #666

Make indexer keep noise about errors that prevent index generation.
Detect certain errors in the APKs better. And also have the applet
return error in these scenarios.

remount to read-write before trying to create the cache directory
subdirs. fix a fd leak that might prevent remounting back to rw.

The apk cache might be on the readonly media so we need wait with
remounting til after atleast this filehandle is closed.

commit 4e72075f introduced a bug where package installation might happen
in wrong order (reminder for self to separate the package version deduction
to separate step from installation ordering). this restricts the earlier
commit to not mingle with the install order.

This is so we can do x86 --root installs on x86_64 hosts.

Using --arch without --root can make great damage so we only enable it
if --root is used.

Parse these fields from .PKGINFO, and write them to index.

Our build infra does not yet handle properly noarch, so for the
time being we will rewrite them as native packages in index. This
allows the package to be fetched from the proper URL. This feature
will be removed once abuild and the build infra handle noarch
properly.

improves behaviour under certain corner case conditions.

The db parameter to apk_state_commit is not needed so we remove it.

Implement the logic for install_if lines. Update info applet to
also display the install_if related fields.

broke after making the version field an atom because the printf
was not updated accordingly.

commit 4e72075f introduced late locking for top level packages,
but used the wrong package's top level flag for the check. this
fixes a problem that dependencies might not get pulled in.